This relates generally to graphics processing and, particularly, to rendering images.
In rendering, an image is represented by primitives, such as triangles or other polygons. A render target is established in a frame buffer. The render target is a destination surface in memory where render results are written. The render cache is a cache in which pixel color and depth information is written prior to being written to memory and where the prior pixel destination attributes are read in preparation for blending and depth tests.
Allocation is the process of allocating a cache line in the render cache. In some cases, the allocation happens for every 2×2 pixel group written from a pixel shader. The group of 2×2 pixels is called a subspan. An unlit bit in a subspan is a pixel that is not enabled in a group of 2×2 pixels.
Typically, in order to save power and improve performance, a frame buffer compression technique is used. The technique relies on tracking unmodified or recently rendered cache lines in the render cache. The unmodified lines can be displayed directly from a compressed buffer.